1. Field of the Invention
The present invention relates to a technology in which a server apparatus acquires information from an information source in response to a request received from a client apparatus, and transmits the acquired information to the client apparatus.
2. Description of the Related Art
In Japanese Patent Application Laid-Open No. H10-032648, a method for automatically updating information of a client/server system is disclosed. In the method for automatically updating information, before a communication call is connected between a client apparatus and a server apparatus, pieces of individual identification information are notified from the client apparatus to the sever apparatus. The server apparatus memorizes records of updated information for the client apparatus. Moreover, the server apparatus determines whether information to be updated for any client is present from among the pieces of individual identification information notified upon an access from the client apparatus, and if it can be determined that no information to be updated is present, suspends connection of a call of telecommunication equipment. Moreover, when communication between the client apparatus and the server apparatus becomes possible, the state is notified from the client apparatus to the sever apparatus, and when service information corresponding to the client apparatus is updated at the side of the server apparatus, the state is notified from the server apparatus to the client apparatus.
Moreover, in Japanese Patent Application Laid-Open No. 2000-090128, an information distribution system is disclosed. In the information distribution system, when any information item is selected as a display target in each of client apparatuses, the information item is registered to a server apparatus. When information of any information item is updated, the server apparatus notifies information reception to a client apparatus which registers the information item, and delivers the received information to the client apparatus, while the client apparatus displays the information item.
A client apparatus, when intending to acquire and display information in real time which is updated irregularly in an information source, needs to execute processing of transmitting a request and receiving a response every given time interval with a sever apparatus. FIG. 5 is a view conceptually illustrating a conventional request/response type communication state. A client apparatus 100 has a client screen 100a and a client communication interface 100b, which requests a server apparatus 101 to transmit information (step S01). Upon reception of the request from the client apparatus 100, the server apparatus 101 checks an information source 102 holding information whether the information is updated (step S11, S12). Here, it is assumed that the information in the information source 102 is not updated.
The server apparatus 101, regardless whether the information in the information source 102 is updated or not, instantly responds to the client apparatus (step S02) Here, a response indicating that the information in the information source 102 is not updated will be made. If the client apparatus 100 transmits a request to the server apparatus 101 again (step S03), the server apparatus 101 checks the information source 102 whether the information is updated (step S13, S14). Since the information in the information source 102 is not updated yet, the server apparatus 101 instantly transmits a response indicating that the information in the information source 102 is not updated (step S04).
Next, as illustrated in FIG. 5, after step S14 and at the time of A0, it is assumed that the information in the information source 102 is updated. If the client apparatus 100 transmits a request to the server apparatus 101 again (step S05), the server apparatus 101 checks the information source 102 whether the information is updated (step S15, S16). Since the information in the information source 102 is updated, the server 101 transmits to the client apparatus 100 information indicating that the information in the information source 102 is updated and information corresponding to the request as a response thereto (step S06). Thus, in the client apparatus 100, at the time of B0, the updated information can be reflected on the screen.
However, according to the conventional method, difference between timing of updating the information in the information source 102 and timing of transmitting a request from the client apparatus causes a state to occur, in which the client apparatus 100 cannot acquire the updated information in real time. That is, as illustrated in FIG. 5, although the information in the information source 102 is updated at the time of A0, the request from client apparatus 100 will be transmitted after that. Thus, in the client apparatus 100, until the updated information is reflected on the screen, time difference as indicated by an arrow “a” will occur. Since, delay in information acquisition will occur in such a way, in the conventional method, it is difficult for the client apparatus 100 to acquire and display information in real time, which is updated irregularly in the information source 102.
Moreover, although it is not impossible to improve real-time performance by shortening processing time interval of server/client communication processing, shortening the processing time interval causes the number of communications to increase, resulting in increase of a network load.
The present invention is made in view of such circumstances, and an object of the present invention is to provide a server apparatus and a communications system in which a client apparatus can acquire information in real time, which is irregularly updated in an information source.